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New Strategy Stops Smallpox in Its Tracks

Drug may stymie virus replication once it's inside cells

WEDNESDAY, Feb. 2, 2005 (HealthDayNews) -- Researchers report that they've been able to stop a smallpox-like virus in mice in just eight days, a development that could lead to more effective treatments for other kinds of illnesses in humans.

While the treatment is not ready for use in people, "it represents a new approach toward antiviral therapies," said Dr. Ellis Reinherz, a researcher at the Dana-Farber Cancer Institute and co-author of the study in the February issue of the Journal of Clinical Investigation.

Doctors banished the deadly smallpox virus from the earth in the 1970s, and universal vaccination against the disease was suspended. But experts fear that terrorists could spread smallpox, and the vaccine that prevents infection can cause fatal side effects, especially in those with weakened immune systems.

In the study, Reinherz and his colleagues used an experimental cancer drug known as a "small molecule" to block the pathways within cells that smallpox targets as part of its hijacking process. Without access to the pathway, the virus can't use the cell's machinery to replicate itself.

In the laboratory, the treatment successfully prevented the smallpox virus from spreading from monkey kidney cells to other cells.

And in live mice infected with a smallpox-like virus, the treatment -- along with an injection of immune system boosters known as antibodies -- helped vanquish the virus in just eight days.

By contrast, other antiviral treatments -- including those that target AIDS -- focus on trying to keep the virus out of cells in the first place.

"Here we're going in the other direction," Reinherz said.

Researchers could conceivably try to block similar routes in all kinds of viruses, including the one that causes AIDS, said Dr. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, who wrote a commentary that accompanied the study in the journal. "You figure out the pathway, and then just see if there are any compounds that can interfere with the pathway in question."

The treatment may also help researchers to make better use of vaccines as potential carriers for cancer-fighting agents, Reinherz added. Researchers have experimented with piggybacking the agents on top of vaccines, allowing them easy access to the body, but the hitch is that vaccines often cause side effects.

"This is one reason to want to study these viruses, even though it may appear that much of the concern (over smallpox) has been alleviated over the years," Reinherz said.

More information

Learn more about smallpox from the U.S. Centers for Disease Control and Prevention.

SOURCES: Ellis Reinherz, M.D., researcher, Dana-Farber Cancer Institute, and professor, medicine, Harvard Medical School, both in Boston; Anthony S. Fauci, M.D., director, National Institute of Allergy and Infectious Diseases, Bethesda, Md.; February 2005 Journal of Clinical Investigation
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